Preparation of norbornene-type monomers is well known. Dicyclopentadiene can be made by dimerizing cyclopentadiene by the Diels-Alder reaction whereas dihydrodicyclopentadiene can be made by the Diels-Alder reaction of cyclopentadiene and cyclopentene. Norbornenes can also be prepared by the Diels-Alder reaction of cyclopentadiene with selected olefins to yield either norbornene or substituted norbornenes. Tetracyclododecene compounds are by-products formed from the Diels-Alder reaction of cyclopentadiene and norbornenes. Symmetrical and unsymmetrical trimers and tetramers of cyclopentadiene can, likewise, be prepared by the Diels-Alder reaction of cyclopentadiene.
Polymeric materials prepared from monomers containing norbornene moiety, i.e. cyclicolefins, can be made as elastomers, which are flexible at room temperature, or as plastics, which can be rigid at room temperature. They can be calendered and thermoformed to make rigid automotive products such as glovebox covers, hubcaps, and other automotive and nonautomotive products.
More specifically, polymers of cyclic olefins can be prepared by ring opening polymerization of the olefins in the presence of a metathesis catalyst comprising at least one alkylaluminum halide cocatalyst and at least one tungsten or molybdenum compound catalyst, preferably tungsten or molybdenum halide. This is accomplished by mixing the cyclic olefins with a hydrocarbon solvent and charging the mixture to a reactor. A molecular weight modifier selected from nonconjugated acyclic olefins is then added to the reactor followed by an alkylaluminum halide cocatalyst and at least one tungsten or molybdenum compound that serves as a catalyst. The catalyst is added as a solution in an alkylester of a saturated carboxylic acid. The polymerization reaction can be conducted at about 0.degree. C. to 200.degree. C., preferably 25.degree. C. to 100.degree. C., with stirring and produces little heat. The reaction time to completion is short, i.e., on the order of less than two hours, and the reaction products are smooth, viscous materials comprising a polymer dispersed in a solvent. The reaction is shortstopped by addition of an alcohol, such as ethanol.
The reason for solubilizing the tungsten or molybdenum catalyst in an alkylester solvent is due to the fact that the catalyst is essentially insoluble in the hydrocarbon reaction solvent. The necessity of preparing a solution of the catalyst in an alkylester solvent is not only costly, time consuming, and requires an additional step, but also presents a dilemma in a continuous polymerization process. As such a continuous process proceeds, the small amount of the alkylester solvent accumulates over a period of time requiring procedures for its removal.
There are other disadvantages inherent in the present process for polymerizing cyclic olefins. Since the tungsten or molybdenum catalyst is unstable in air and degrades in presence of moisture, special precautions must be taken to prevent its contact with air and humidity. In presence of water, the catalyst reacts to form a hydroxide and hydrochloric acid, which is corrosive to metal piping, pumps and any other metal materials it contacts.
There is another problem with the tungsten or molybdenum catalyst as it is presently used. The catalyst, when mixed with a monomer, causes very slow although significant polymerization of the monomer over longer periods of time. This is undesirable since it is of a definite advantage to have a totally inactive catalyst until the alkylaluminum halide cocatalyst is added. In certain applications, process design is formulated on the principle of storing a monomer and a catalyst in one tank and a monomer and the alkylaluminum halide cocatalyst in another tank whereby the mixtures from the two tanks are separately conveyed to a reactor and mixed therein to initiate the reaction. Due to slight polymerization of the monomer in presence of the salt catalyst, such process design is rendered impractical.
Last, but not least, the tungsten or molybdenum catalyst currently in use is not soluble in the monomer. As is well known, it is of paramount importance in certain polymerization procedures, such as bulk polymerization and reaction injection molding, that the catalyst be soluble in the monomer. Unless the catalyst is soluble in the monomer, these procedures cannot be carried out in a practical manner.